1. Field of the Invention
The present invention relates generally to greenhouses. More specifically, the present invention relates to devices that allow the user to cover and uncover the top of a greenhouse at will.
2. Discussion of Background
A greenhouse is a lightweight enclosure that provides covering for plants and seedlings, whether planted in flowerpots or trays or in the earth enclosed by the greenhouse. Typically, a greenhouse comprises a framework and a covering. The framework can be made of metal, wood or plastic; and the covering can be made of glass, flexible plastic sheeting or panels. Invariably, the covering is light-transmitting although not necessarily light-transparent and is most often "fixed"; that is, it remains permanently in place and is not easily openable or removable. For ventilation, greenhouse will often have louvers, perhaps, with assisted by large fans, on the ends.
The purpose of the greenhouse is to protect the plants and seedlings from the extremes of the environment: excessive heat or cold, excessive amounts of rain or "hard" rains. However, greenhouses can also cause problems for growing plants. They trap heat, for example. Also, because plants naturally grow toward the light--a tendency known as phototropism --and because greenhouse coverings invariably attenuate the light, plants in greenhouses can tend to be spindly.
Ideally, greenhouses should have a cover that can be opened when the weather is clear and warm, and that can be closed on nights when the temperature is expected to drop to unacceptably low levels, or on days when it will rain excessively or rain hard, or when too much heat has built up in the greenhouse. Such a cover would not only help to regulate the temperature within the greenhouse, but would reduce watering costs and make plants healthier, thicker and fuller.
There are greenhouses that can be opened up or uncovered. Theoretically, greenhouses can have windows similar to those in homes. However, it is simply not practical to incorporate ordinary windows into greenhouse designs. First, a system for uncovering a greenhouse must be simple structurally so that it is not cost-prohibitive. It must be easy to use so that greenhouses can be uncovered and covered quickly and without special training. Furthermore, commercial greenhouses often cover several acres of ground. If the closure mechanism is too complicated or slow, operating it may require extensive manpower or time or both. Finally, if the covering for the greenhouse is made of plastic, the covering mechanism must accommodate the characteristics of plastic. These characteristics include (1) a tendency to "bathtub" or collect water where the plastic sags, (2) the tendency to catch the wind and (3) limited structural strength.
However, the advantages of a system that can meet this requirement are considerable. An inexpensive, easy to use and reliable system for covering and uncovering the greenhouse can make growing of plants much easier and result in higher quality plants, better yields and lower costs. Moreover, such a system is not limited to use as greenhouses. Temporary structures for out-of-door events can also benefit from such a mechanism.
There remains a need for a covering mechanism for greenhouses that operates easily and simply and does not add undue cost to the overall cost of greenhouse construction.